Antioxidant composition and synthetic lubricant containing it



United States Patent 3,236,774 ANTIOXIDANT COMPOSITION AND SYNTHETICLUBRICANT CONTAINING IT John W. Thompson and Gerald S. Cassell,Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y a corporationof New Jersey No Drawing. Filed Aug. 10, 1962, Ser. No. 216,070 Claims.(Cl. 25246.7)

This invention relates to ester type synthetic lubricants and to theproblem of protecting them from oxidative degradation.

Synthetic lubricants of the ester type have replaced petroleum oils inmany lubricant and hydraulic fluid applications Where severe serviceconditions are encountered. As an example, esters such asbis(2-ethylhexyl)sebacate are used almost universally as lubricants inaircraft turbine engines of the pure jet and prop-jet types. However,under such severe service conditions, these organic esters as a classare very susceptible to oxidation. Consequently, in formulatingsatisfactory jet engine lube oils from esters and the like, measuresmust be taken to protect these esters from oxidative attack under thesesevere service conditions.

Phenothiazine has been one of the most used anti oxidants for ester typesynthetic lubricants. It has been reasonably satisfactory for moderatelyhigh jet engine temperatures. However, as is well-known, phenothiazineis a dirty antioxidant, causing the formation of insoluble sludgesduring lubricant use. In addition to such sludging characteristics,phenothiazine does not appear to stabilize ester lubricantssatisfactorily at the higher temperatures for which current militry andcivil jet engines are being designed. a

A problem, therefore, to which this invention provides a solution is howto minimize, if not eliminate, the sludging characteristics ofphenothiazine under the more severe service conditions and particularlyhigher temperatures, as well as to increase the stabilizing action ofthe phenothiazine at these higher temperatures.

This invention is based upon the discovery that small amounts of acidicphosphorus compounds greatly improve the antioxidant properties ofarylamine type antioxidants and particularly phenothiazine in ester lubeoils for aircraft jet engines. The acidic phosphorus compounds have beenfound to retard the sludging or dirtiness caused by the arylamineantioxidants and to increase the antioxidant action or stabilizingaction of the arylamine antioxidants.

I" In summary, this lnvention comprises an antioxidant compositionparticularly useful for ester type synthetic lubricants. In addition,this invention broadly comprises an ester type synthetic lubricantcontaining the antioxidant composition at an efiective or protectiveconcentration.

The antioxidant composition of this invention comprises a mixtureconsisting essentially of an arylamine antioxidant portion and at aminor concentration relative to the arylamine antioxidant portion anacidic phosphorus portion. The arylamine antioxidant portion of thecomposition consists essentially of at least one arylamine antioxidant.Examples of an arylamine antioxidant include phenothiazines such asphenothiazine, phenothiazine derivatives containing substituents on thenitrogen atom and phenothiazine derivatives containing substituents onthe rings, alkylated diphenylamines, N-phenylnaphthylamines anddinaphthylamines. Prefered arylamine antioxidants includeN-alkylphenothiazines wherein the N-alkyl group has 1-18 carbon atoms,N-phenyl-l-naphthylamine and p,p'-dialkyl diphenylamines such asp,p'-dioctyldiphenylamine, wherein the p and p-alkyl groups each have1-18 carbon atoms. In preferred embodiments of this invention thearylamine antioxidant portion consists essentially of a mixture of anN-alkylphenothiazine and a p,p-dialkyldipldienylamine. Typical examplesof such a mixture inc u e:

N-ethylphenothiazine and p,p'-dioctyldiphenylamine N-butylphenothiazineand dinonyldiphenylamine N-octylphenothiazine andp,p'-dibutyldiphenylamine N-d-odecylphenothiazine andp,p-dioctyldiphenylamine N-ethylphenothiazine andN-phenyl-l-naphthylamine N-acetylphenothiazine andp,p'-dioctyldiphenylamine N-methylphenothiazine andN-phenyl-Z-naphthylamine N-decylphenothiazine and diphenylamineN-ethylphenothiazine and di-l-naphthylamine The weight ratio of theN-alkylphenothiazine to the p,p'- dialkyldiphenylamine is generally in arange from about 1:3 to about 3:1 and preferably in a range from about2:3 to about 3:2.

The acidic pohsphorus portion of the antioxidant composition of thisinvention consists essentially of at least one acidic phosphoruscompound. This is a compound having at least one acid (OH) groupattached to a phosphorus atom. Such a compound is present in phosphoricacid, phosphorous acid and organic partial esters of these acids. Theorganic partial esters of these acids are preferred since they are moresoluble in the esters normally employed as synthetic lubricants, and areless extractable therefrom by aqueous solutions. The organic partialesters of phosphoric acid include alkyl dihydrogen phosphates, dialkylhydrogen phosphates, aryl dihydrogen phosphates, diaryl hydrogenphosphates, alkylaryl dihydrogen phosphates and di(alkylaryl)hydrogenphosphates. It is preferred that the alkyl groups in these compoundsthat have such contain 18 carbon atoms. The organic partial esters ofphosphorous acid include alkyl dihydrogen phosphites, dialkyl hydrogenphosphites, aryl dihydrogen phosphites, diaryl hydrogen phosphites,alkylaryl dihydrogen phosphites and di(alkylaryl)hydrogen phosphites.Here, too, it is prefered that the alkyl groups in these compounds thathave such contain 1-8 carbon atoms. Under the concepts of this inventionthe acidic phosphorus portion of the antioxidant composition of theinvention can consist essentially of a mixture of acidic phosphoruscompounds. Generally, the acidic phosphorus esters are obtainedcommerically as mixtures of the monoalkyl and dialkyl derivatives andare referred to as alkyl acid phosphates and alkyl acid phosphites.These mixtures are within the concepts of this invention. Preferred,specific, acidic phosphorus compounds include ethyl acid phosphate,butyl acid phosphate, methyl acid phosphate and phosphorous acid.

Concentration of the arylamine antioxidant portion of the mixture whichcharacterizes the antioxidant composition of this invention is generallygreater than the concentration of the acidic phosphorus portion of themixture. Usually, concentration of the arylamine antioxidant portion isbroadly in a range from about 95.3 to about 99.95 by weight of themixture and preferably in a range from about 97.6 to about 99.75.Concentration of the acidic phosphorus portion of the mixture usually isbroadly in a range from about 0.05 to about 4.7% by weight of themixture and preferably in a range from about 0.25 to about 2.4% byweight of the mixture.

The antioxidant composition is prepared by admixing the componentsthereof until a uniform blend is obtained.

The synthetic lubricant of this invention consists essentially of anorganic ester base stock and at a protective concentration theantioxidant composition of this invention.

The organic ester base stock consists essentially of at least oneorganic ester which is an oil at 20 C. Such an ester is provided byvarious diesters of dibasic acids and alcohols, diesters of monobasicacids and glycols, triesters of monobasic acids and trihydric alcoholssuch as trimethylolethane, trimethylolpropane and the like,pentaerythritol tetraesters, and polyesters such as those obtained froma dibasic acid and a glycol and chain terminated with either an alcoholor a monobasic acid. Typical organic esters include:

2-butyl-2-ethyll ,3-propanediol dipelargonate2-ethyl-2-isobutyl-l,3-propanediol diundecanoate2,2-diethyl-l,3-propanediol dipelargonateBis(2,2,4-trimethylpentyl)azelateBis(2,2,4-trimethylpentyl)undecanedioate Bis2-methyl-2-norcamphanylmethyl sebacate 1,l-cyclopentanedimethanoldipelargonate Trimethylolpropane triheptanoate Pentaerythritoltctrahexanoate Bis(2-ethylhexyl)sebacate Esters of alcohols and oleicacid dimers and trirners Polyester of azelaic acid, neopentyl glycol and2,2,4-trimethylpentanol at a mole ratio of 1:1:0.25

Polyester of azelaic acid, 2-butyl-2-ethyl-1,3-propanediol and octanoicacid at a mole ratio of 1:1:0.25

Concentration of the antioxidant composition of this invention in thesynthetic lubricant in general depends upon the ester base stock and onthe degree of stability desired. However, in general, a concentration ofthe antioxidant composition in a range from about 0.1005 to about 5.2%by weight of the ester base stock and preferably in a range fro-m about0.201 to about 4.05% by weight of the ester base stock givessatisfactory results. At these concentrations, the concentration of thearylamine antioxidant portion of the antioxidant composition is in ageneral range from about 0.1 to about by Weight of the ester base stockand preferably in a range from about 0.2 to about 4% by weight of theester base stock. Similarly, at these concentrations, the acidicphosphorus portion of the antioxidant composition is present at aconcentration in a general range from about 0.0005 to about 0.2% byweight of the ester base stock and preferably in a range from about0.001 to about 0.05% by weight of the ester base stock.

Besides the ester base stock and antioxidant composition, the syntheticlubricant of this invention can also comprise other additives such aslubricity improvers, anticorrosion agents, metal deactivators,detergents, dyes and phenolic antioxidants.

The synthetic lubricant of this invention is prepared merely by admixingthe components thereof until a uniform blend, usually in the form of asolution, is obtained. In admixing the components of the syntheticlubricant, the antioxidant composition can be added as such to the esterbase stock or the components of the antioxidant composition can beindividually added to the ester base stock whereby the antioxidantcomposition is formed in the ester base stock.

The synthetic lubricant of this invention is suitable for a variety ofsevere service uses. Indeed specific embodiments thereof satisfymilitary and civil jet engine specifications such as MILL7808D,MILL25,336, MIL-L9236B, MILL27,502, DERD 2487 and others. In additionthe synthetic lubricant has utility under less severe service conditionsas a hydraulic fluid, industrial lubricant, coolant fluid and automotivelubricant.

This invention is further illustrated by the following examples ofvarious aspects thereof, including preferred specific embodiments of theinvention. This invention is not limited to these specific embodimentsunless otherwise indicated.

Specific embodiments of the antioxidant composition of this inventionare formulated as follows:

EXAMPLE 1 Components: Parts by Weight N-ethylphenothiazinep,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.1

EXAMPLE 2 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Ethyl acidphosphate 0.5

EXAMPLE 3 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Ethyl acidphosphate 0.75

EXAMPLE 4 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 Ethyl acidphosphate 1 EXAMPLE 5 Components:

N-ethylphenothiazine 100 p,p'-Di0ctyl-diphenylamine 100 Ethyl acidphosphate 2 EXAMPLE 6 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 Ethyl acidphosphate 10 EXAMPLE 7 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Dodecyl acidphosphate 1 EXAMPLE 8 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3propanediol cyclic hydrogen-phosphate 0.6

EXAMPLE 9 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 o-Phosphoricacid 0.36

EXAMPLE 10 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 o-Phosphoric acid0.42

EXAMPLE 11 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3propanediol cyclic hydrogen-phosphite 1 EXAMPLE 12 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Diethyl hydrogenphosphite 0.44

EXAMPLE 13 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Bis(2-ethylliexyl)hydrogen phosphite 1 3 K EXAMPLE 14 Components: Parts by weightN-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Ethyl acidphosphate 1 EXAMPLE 15 Components:

N-ethylphenothiazine 100 N-phenyl-l-naphthylamine 100 Ethyl acidphosphate 0.5

EXAMPLE 16 Components:

N-ethylphenothiazine 100 p,p' Dioctyldiphenylamine 100 Butyl acidphosphate 1.3

EXAMPLE 17 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Diphenyl hydrogenphosphate 1.2

EXAMPLE 18 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Methyl acidphosphate 0.6

Each one of the antioxidant compositions of the foregoing specificformulations are prepared merely by admixing the components at roomtemperature until a uniform blend is obtained.

Specific embodiments of the synthetic lubricant of this invention areformulated as follows.

EXAMPLE 19 Components: Parts by weight Ester basestock2-buty1-2-ethyl-1,3-propanediol dipelargonate 10,000 Antioxidantcomposition N-ethylphenothiazine -l00 p,p'-Dioctyldiphenylamine 100Ethyl acid phosphate 0.1

EXAMPLE 20 Components:

Ester base stock-2-butyl-2-ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.5

EXAMPLE 21 Components:

Ester base stock2-butyl-2-ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition- N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.75

EXAMPLE 22 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,00Antioxidant composition N-ethylphenothiazine 100p,p'-Dioctyldiphenyl-arnine 100 Ethyl acid phosphate :1

EXAMPLE 23 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition- N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 2 6 EXAMPLE 24Components: Parts by weight Ester base stock2 butyl 2ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant compositionN-ethylphenothiazine p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate10 EXAMPLE 25 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 Dodecyl acid phosphate 1 EXAMPLE 26Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol-cyclichydrogen-phosphate 0.6

EXAMPLE 27 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p'-Diocty1diphenylamine 100 o-Phosphoric acid 0.36

EXAMPLE 28 Components:

Ester base stock-2 butyl 2 ethyl-1,3-pr0- panediol dipclargonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p'-Dioctyldipheny1amine 100 o-Phosphoric acid 0.42

EXAMPLE 29 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipel-argonate 10,000Antioxidant composition N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol-cyclichydrogen-phosphite 1 EXAMPLE 30 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition N-ethylphenothiazine 100 Samples 615 in Table I,it will be noted, have the anti- Diethyl hydrogen phosphite 0.44

EXAMPLE 31 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000Antioxidant composition- N-ethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 Bis(2-ethy1hexyl)hydrogen phosphite 1 7EXAMPLE 32 Components: Parts by weight Ester base stock2 butyl 2ethyl-1,3-propanediol dipelargonate Antioxidant composition 8 EXAMPLE 37Components: Parts by weight Ester base stookBis(2,2,4-trimethylpentyl)azelate 10,000 Antioxidant composition N-dodecylphenothiazine 100N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100p,p'-D1octyldiphenylamlne 100 Ethyl acid phosphate 1 Ethyl ac1dphosphate 1 EXAMPLE 38 EXAMPLE 10 Components: Components: Ester basestock1lrimethylolpropane tri- Ester base stock2 butyl 2ethyl-1,3-p1oheptanoate 10,000

panediol dipelargonate 10,000 Antioxidant composition Antioxidantcomposition- N-ethylphenothiazine 100 Nethylphenothiazine 100p,p'-Dioctyldiphenylamine 100 N-phenyl-l-naphthylamine 100 Ethyl acidphosphate l Ethyl and phosphate The synthetic lubricant compositions ofthe foregoing formulations are prepared merely by admixing the variousEXAMPLE 34 components specified in the formulations. Such mixingcomponents! is preferably undertaken at room temperature and is EsterP2186 Y Y s 'P continued until the components of the antioxidant com- PF dlpelargqqate 10,000 position are dissolved in the ester base stock.

AntlOXldaHt P The effectivenes of the antioxidant composition of this ev p q 100 25 invention and the stability of the. synthetic lubricant ofPBP Q Y P Y 100 this invention are demonstrated by the following testdata Butyl acld Phosphate obtained in actual tests on samples ofsynthetic lubricants formulated as indicated in the following tables.The EXAMPLE tests and measurements employed in the testing are asComponents: 30 follows.

Ester base stock-2Hbutyl-2-ethyl-L3-pro- AF oxzdatzon test i fdlpel'aTgqllate 10,000 This test, which indicates the oxidationstability of the Annoxldant f P synthetic lubricant at hightemperatures, is described in N"3,thY lPhen" th1aZme 1 100 a paperentitled Materials for High Temperature Jet P 'Dloctyldlphenylamme 10039 Engine Lubricants (H. E. Adams) in W.A.D.C. Tech Drphenyl hydrogenphosphate nical Report 59244 (Air Force, 1959). The test conditionsemployed in this test are selected to simulate high EXAMPLE 36temperature jet engine and bearing rig operation condi- Components:tions.

Ester base st0ck-2 butylr2-ethyl-l,3-pro- 40 In this test a 250milliliter sample of the lubricant is paned-iol dipelargonate 10,000heated at 425 F. in a Pyrex test tube while 96 liters of Antioxidantcomposition air per hour are blown through it. A freshly polishedN-ethylphenothiazine 100 metal panel is immersed in the lubricant. Thetest tube is p,p'-Dioctyldiphenylamine 100 capped with a Pyrex fittingwhich allows volatile products Methyl acid phosphate 0.6 40 to escapefrom the tube. The lubricant in the tube is TABLE I Additives Viscosityacid N 0. at- Sludge rating (hours) Sample Gone. in Gone. in

N 0. percent Acidic phosphorus percent Arylamines by wt. compound by wt.120 hrs. 120 hrs. 20 40 of ester of ester base stock base stock 1 No11eNone 104.7 12.4 0

(at 20 hrs.) (at 20 hrs.) N-ethylphenothiazine 2 d0.. 23.8 5. 26 8 10 10(at 60 hrs.) (at 60 hrs.) p,p-Dioctyldiphenylamine 2 .-..d0 116.5 13.632 N th 1 hen thiaziue (at 20 hm) (at 20 hrs') -8 O p,p-D io t:tyldiphenylam 1e" 0 1 2 G 8 9 None. Ethyl acid phosphate 0.0075 30.9817.14 0 N th 1 hen thia inc 1 (M20 hrs') (M20 his) -e 0 Z i p i g ldinen mmma 1 M01 364 O 0 1 2 8 8 1 11i g g gggfg gg g do 0.005 20.0 3.07 00 0 0 o 2 if i tfilfi lfifiglinnsi i W m 0 0 1 2 3 en f, fi :f 1 d0....0.1 22.3 a. 07 1 1 1 4 4 5 i f fi iggl sfl lgggfg g }Dodecylacidphosphate.-- 0.01 21.2 a. 01 0 1 1 2 3 a N-ethylpheuothiazine 12,2-dimethyl1,3-propane 0.006 22.5 4. 23 1 1 2 3 3 4 diol cyclichydrogen p,p-Dioctyldiphenylaminm. 1 phosphate. 12 g igig ggiflf gfigfgfig }o-Phosphoric acid 0.0030 20.8 3. 20 0 0 0 1 1 1 13 g fi g gfiffigf fi 1 do 0. 0042 22.5 3.27 1 1 1 2 5 4 14 N-ethylphenothiazine 1}Diethyl hydrogen phos- 0.0044 0 0 0 4 p,p-Dioctyldiphenylarnine. 1phite. 15 N-ethylphenothiazino 1 }Bis(2-ethylhexyl) hydro- 0.01 22.03.85 0 0 0 2 3 4 p,p-Dioctyldiphenylaminen 1 gen phosphite.

heated in 20 hour cycles and at the end of each cycle the tube iscooled, a 10 milliliter sample of the lubricant is Withdrawn foranalysis and the lubricant lost by evaporation is replaced with freshlubricant. Ordinarily the test is conducted for 6 cycles or 1 20 hours.The 10 rnil liliter samples are analyzed for viscosity in centistokes at100 F. (ASTM Method D445), acid number (in milligrams of KOH per gram)(ASTM Method D974) sludge content. Sludge content is determined byfiltering a 2 milliliter sample of the lubricant through a Whatman No. 2filter paper (4.25 centimeters), washing the paper with 25 millilitersof Stoddard solvent, drying the paper and then rating the sludge depositon the paper according to a scale from to 10, 0 being equivalent toclean and 10 designating hea-vy deposit.

In the first series of tests the ester base stock in each sampleconsisted essentially of 2-tbutyl-2-ethyl-1,3-propanediol dipel-angonateand was characterized by an acid number (milligrams of KOH per gram) of0.03, a viscosity at 65 F. of 15,084 centistokes, a viscosity at 100 F.of 14.32 centistokes and a viscosity at 210 F. of 3.33 centistokes, anopen cup flash point of 443 F. and a pour point of less than -70 F. Thetest samples containing additives were prepared from this ester basestock and the specific additives at specific concentrations indicated inthe preceding Table I. These test samples were prepared merely byadmixing the additives into the ester base stock until in each case auniform blend was obtained. The metal panels employed in theseparticular tests were made of steel and each had the dimensions: 1 inchby 1 inch by inch. The test results and other test conditions in thisfirst series of tests are set out in the preceding Table 1.

Samples 6-15 in Table I, it will be noted, have the antioxidantcompositions of Examples 1-2, -10 and 12-13, and correspond informulation to the specific synthetic lubricants of Examples 19-20,23-28 and 30-31.

In the case of Samples 1, 3 and 5, the AF oxidation test procedure wasstopped after 20 hours due to the obviously rapid oxidation of thesamples, and viscosity and acid number measurements were then made onthese samples. In the case of sample 2, the AF oxidation test procedurewas terminated after 60 hours, because of the highly oxi- 10 dizedcondition of the sample, and viscosity and acid number measurements werethen made on the sample. All other samples (4 and 6-15), were subjectedto the AF oxidation test for the full 120 hours.

A comparison of the test data of Sample 6 with the test data of Samples1-5 demonstrates the need for an etfective antioxidant composition inthe ester base stock and the fact that the antioxidant composition inSample 6 is effective. Comparison of the data of Samples 6-15 with thedata of Sample 4 reveals the dramatic effect of various acidicphosphorus compounds on the antioxidant activity of the arylamineantioxidant mixture of Sample 4, especially in regard to reduction insludging tendency.

In the next test series summarized in the following Table 11, testsamples of synthetic lubricants were prepared from difierent ester basestocks and with various arylamine antioxidants and ethyl acid phosphate.In this series of tests, the ester base stock identified in Table II asBEPD consisted essentially of 2-butyl-2-ethyl-1,3-propanedioldipelargonate and had an acid number (milligrams of KOH per gram) of0.03, a viscosity at F. of 15,084 centistokes, a viscosity at 100 F. of14.32 centistokes, a viscosity at 210 F. of 3.33 centistokes, an opencup flash point of 443 F. and a pour point of less than F. The esterbase stock identified in Table 11 as TMPZ consisted essentially ofbis(2,2,4-trimethylpentyl) azelate and had an acid number (milligrams ofKOH per gram) of 0.06, a viscosity at 65 F. of 8,940 centistokes, aviscosity .at 100 F. of 13.14 centistokes, a viscosity at 210 F. of 3.45centistokes, an open cup flash point of 425 F. and a pour point lessthan F. The ester base stock identified in Table II as TMPTH consistedessentially of trimethylolpropane triheptanoate and was characterized byan acid number (milligrams of KOH per gram) of 0.07, a viscosity at 65F. of 17,911 centistokes, a viscosity at F. of 16.09 centistokes, a

viscosity at 210 F. of 3.66 centistokes, an open cup flash point of 450F., and a pour point of less than -65 F. The test samples were preparedby admixing the components thereof until solutions Were formed. Themetal panels employed in these particular tests were made of steel andeach had the dimensions: 1 inch by 1 inch by inch. The test results andtest sample formulations are set forth in the following Table II.

TABLE II Sample composition Test results Sample Gone. in Acidic Gone. inHours 0. Ester base Arylarmnes percent by phosphorus percent by Propertystock wt. of ester compound wt. of ester base stock base stock 0 20 4060 80 100 Viscosity" 15.03 17.95 19.64 21.63 23.63 26.48 31.91 1 BEPDN-dodccylphenothiazme 1 }None Acid No 0.05 2.20 3.68 3.46 3.27 4.75 5.36p,p-dioctyldiphenylamme l Sludfige 0 0 0 1 2 2 4 re mg. Viseosity 15.0316.44 17.29 18.36 19.72 20.96 22.48 2 BEPD N-dodecylphenothiazine-. 1}Ethyl acid 001 Acid No 0.14 0.96 1.37 2.08 4.09 2.77p,p-dioctyldiphenylamine 1 phosphate. Sludtge 0 0 0 0 1 1 2 re mg.Viscosity" 15.03 16.17 18.77 3 BEPD N-ethylphenothiazme 1 }None Acid No0.04 1.00 3.44 N-phenyl-l-naphthylamine 1 Sludge 0 6 7 rating. isc0Sity15.03 15.81 20.16 4 BEPD N-ethylphenothiazine 1 Ethyl acid 0 005 Acid No0.10 0.72 4.42 N-phenyl-l-naphthylamine.. 1 phosphate. Sludge 0 2 3 ramg. iseosity 13.58 15. 30 16.38 17.84 19.42 21.61 23.47 5 TMPZN-ethylphenothiazine 1 }None Acid No 0.15 1.69 2. 77 2.64 3.16 3.70 3.66p,p-dioctyldiphenylamine 1 Sludgge 0 0 2 4 6 8 8 In mg. Viscosity 13.5815.07 16.14 17.39 19.30 20.16 22.68 6 TMPZ N-ethylphenothiazine 1 Ethylacid 0 01 Acid No 0.43 0.96 1.99 2.05 3.10 3.19 4.12p,p-dioetyldiphenylamine 1 phosphate. Sludtge 0 0 0 1 3 3 3 ra mg.iscosity 16. 62 20.19 22.40 24.81 28.07 32.09 38.39 7 TMPTHN-ethylphenothiazine 1 }None Acid No 0.03 1.27 1.98 2.55 3.91 3.95 5.52p,p-dioctyldiphenylamine 1 Sludtge 0 0 0 1 2 2 2 ra mg. Viscosity 16.6219.50 20.28 22.85 24.65 26.42 29 38 8 TMPTH N-ethylphenothiazine 1 Ethylacid 0 01 Acid No 0.23 0.95 1.51 2.09 2.91 2 87 3.17p,p-dioctyldiphenylamine 1 phosphate. Sludtge 0 0 0 0 1 l l ra mg.

1 1 Sample 2 in Table II has the specific antioxidant composition ofExample 14 and corresponds in formulation to the specific syntheticlubricant of Example 32. Sample 4 in Table II has the specificantioxidant composition of oxidant compositions of Examples 17 and 18,respectively, and corresponded in formulation to the specific syntheticlubricants of Examples 35 and 36, respectively.

These data of Table III dramatically illustrate the bene- Example 15 andcorresponds in formulation to the specific 5 ficial efiect of acidicphosphorus compounds on arylsynthetic lubricant of Example 33. Samples 6and 8 amine antioxidants in stabilizing synthetic lubricants of have thespecific antioxidant composition of Example 4 the ester type. These datashow that acidic phosphorus and correspond in formulation to thespecific synthetic compounds substantially reduce sludging of synthet1clubricants of Examples 37 and 38, respectively. lubricants of the estertype, when containing arylamlne These data of Table II demonstrate theoutstanding 10 antioxidants. effectiveness .of the various specificembodiments of the Thus, there is provided an antioxidant compositionantioxidant composition of this invention in protecting which isparticularly useful for synthetic lubricants of several different esterbase stocks from oxidative attack, the ester type, which are intendedfor severe servlce and particularly in reducing sludging. In addition,these use. Moreover, there is provided a synthetic lubricant datademonstrate the outstanding stability of a number which has a highdegree of protection relat1ve to oxidaof specific embodiments of thesynthetic lubricant of this tive degradation, particularly under severeservice coninvention. ditions.

In the next series of tests which are summarized in the Other features,advantages and specific embodiments following Table III the ester basestock that was used of this invention will be apparent to those in theexercise consisted essentially of 2-butyl-2-ethyl-1,3-propanediol diofordinary skill in the art after reading the foregoing pelargonate andwas characterized by an acid number disclosure. In this connection,while this IHVCIllZlOIl has (milligrams of KOH per gram) of 0.03, aviscosity at been described in considerable detail relative to spec1ficof 15,054 Centistokes, t1 Viscosity at 00 F. of embodiments thereof,variations and modifications of 14-32 Centistokes, a Viscosity at Of -33C tithese specific embodiments can be effected within the Stokes, an p pas point 0f 4 3 F. and a pour point spirit and scope of the invention asdisclosedand claimed. of 1655 than TO test Samples of this Stock WereThe embodiments of the invention in which an excluaddedN'etbylpbenothiazine and PM- y p y sive property or privilege is claimedare defined as follows: amine, the concentration of each one of thesearylamines 1 A ti idant composition comprlsing a mixture in the esterbase Stock being 1% y Weight of the ester consisting essentially of (1)an arylamine antioxidant porbase stock. Where indicated in the followingTable III, i consisting e entially of (a) N-alkylphenothiazlne specificacidic phosphorus compounds were added to h i h N- 1k 1 group h .143carbon atoms and various ones of the test samples. In each case theaddi- (b) -d-ialkyldi henylamine wherein the p and p -alkyl tives andester base stock were admixed until a solution ou each have 1-18 carbonatoms, the vvelght 111 1 f was formed. In the stability testing of thesetest samples, th N-alkyl-phenothiazine to the p,p-d1alkyld1phenyl thedegree of metal to lubricant contact was increased by amine b i i arange f bo t 1: 3 to about 3:1, and replacing the smaller metal panelswith larger metal panels 2) an acidic phosphorus portion consistingessentially (11/2 inches y 6 inches y /16 inch) and y using both of atleast one acidic phosphorus compound selected from steel and aluminumpanels except where otherwise indithe group consisting of an alkyl acidphosphate wherein cated. Formulations of the various test samples andtest the alkyl group contains from 1 to 10 carbon atoms, 0- results areset out in the following Table III. phosphoric id, diphenyl hydrogen hhate, d ethyl TABLE III Gone. in Hours Sample Acidic phosphorus compoundpercent by Metal panels used Property No. wt. of ester base stock 0 2040 Viscosity 15. 03 23. 03 31.13 42.96 N m teel only {Acid N0 0.04 5.559.06 17.97

Sludge rating. 0 1 4 6 Viscosity 15. 03 24.80 37. 59 56.36 95.72 2.None... Steel plus a1uminum {Acid No 0.04 6.55 9.65 10.49 10.71 Sludgerating. 0 3 3 6 iscosity 15. 03 16.20 17.05 18.06 19.16 .35 21.72 3Ethyl acid phosphate 0.0075 do {Xcid No 0.11 0.69 1.16 1.38 1.84 3.383.12 Sludge rating. 0 1 0 0 1 1 1 Viscosity 15. 03 16.47 17.21 18.4419.59 21.01 22.60 4 Butyl acid phosphate 0.013 (10 {Acid No 0.12 2.461.75 1.96 1.53 3.19 Sludge ratin 0 2 2 2 2 2 2 4 Viscosity 15. 03 16.2817.15 18.25 19.86 21.06 22.73 2,?rd1rnethyl-1,3-propa11ed1ol- 5cyclie-hydrogen-phosphite. {g gg gg 3 3 3 8 2 Viscosity 14. 91 16.1717.03 18.11 19.01 20.05 21.47 6 Diphenylhydrogenphosphatc. 0.012 .d0{Acid No 0.21 1. 26 1. 64 1.89 2.57 3.27 Sludge rating. 0 1 2 2 3 5 6iscosity .14.91 16.17 17.08 17.73 18.41 19.41 20.95 7 Methyl acidphosphate 0.006 do {from No 0.14 1.38 2.10 2.46 2.15 3.27 3.40 Sludgerating- 0 0 0 0 O 0 2 Sample 3 of Table III, it will be observed, hadthe antioxidant composition of Example 3 and corresponded in formulationto the specific synthetic lubricant of Example 21. Sample 4 containedthe antioxidant composition of Example 16 and corresponded informulation to the specific synthetic lubricant of Example 34. Sample 5had the antioxidant composition of Example 11 and corresponded informulation to the specific synthetic lubricant of Example 29. Samples 6and 7 contained the antihydrogen phosphite, bis(2-ethyl hexyl)hydrogenphosphite and 2,2-dimethyl-1Q3 propanediol-cyclic-hydrogenphosphite, theconcentration of said arylamine antioxidant portion being in a rangefrom about 95.3 to about 99.95% by weight of said mixture and theconcentration of said acidic phosphorus portion being in a range fromabout 0.05 to about 4.7% by weight of said mixture.

2. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of (a) N-alkylphenot hiazine wherein the N-alkyl group has1-"18 carbon atoms and (b) p,p'-dialkyldiphenylamine wherein the p andp-alkyl groups each have 1- 18 carbon atoms, the weight ratio of theN-a'lkylphenothiazine to the p,p-dialkyldiphenylamine being in a rangefrom about 2:3 to about 3:2, and (2) an acidic phosphorus portionconsisting essentially of at least one acidic phosphorus compoundselected from the group consisting of an alkyl acid phosphate whereinthe alkyl group contains from 1 to 10 carbon atoms, o-phosphoric acid,diphenyl hydrogen phosphate, diethyl hydrogen phosphite,bis(2-ethylhexyl)hydrogen phosphite and 2,2- dilmethyl 1,'3=propanediol-cyclic hydrogen-phosphite, the concentration of saidarylamine antioxidant portion being in a range from about 97.6 to about99.75% by weight of said mixture and the concentration of said acidicphosphorus portion being in a range from about 0.25 to about 2.4% byweight of said mixture.

3. An antioxidant composition comprising a mixture consistingessentially of ('1) an arylamine antioxidant portion consistingessentially of N-ethylp-henothiazine and p,p'-dioctyldiphenylamine, theWeight ratio of said N-ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range-from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of at leastone acidic phosphorus compound selected from the group consisting of analkyl acid phosphate wherein the alkyl group contains from 1 to 1 carbonatoms, o-phosphoric acid, diphenyl hydrogen phosphate, diethyl hydrogenphosphite, bis(2-ethylhexyl) hydrogen phosphite and 2,2- dirnethyl 1,3propanediolcyclic-hydrogen-p hosphite, the concentration of saidarylamine antioxidant portion being in a range from about 97.6 to about99.75% by Weight of said mixture and the concentration of said acidicphosphorus portion being in a range from about 0.25 to about 2.4% byweight of said mixture.

4. An antioxidant composition comprising a mixture consistingessentially of 1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, theWeight ratio of said N- ethylphenot hiazine to saidp,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of ethylacid phosphate, the concentration of said arylamine antioxidant portionbeing in a range from about 97.6 to about 99.75% by weight of saidmixture and the concentration of said acidic phosphorus portion being ina range from about 0.25 to about 2.4% by Weight of said mixture.

5. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-et'hylphenothiazine and p,p-dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,.and (2) an acidic phosphorus portion consisting essentially of dodecylacid phosphate, the concentration of said arylamine antioxidant portionbeing in a range from about 97.6 to about 99.75% by weight of saidmixture and the concentration of said acidic phosphorus portion being ina range from about 0.25 to about 2.4% by weight of said mixture.

6. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially ofo-phosphoric acid, the concentration of said arylamine antioxidantportion being in a range from about 97.6 to about 99.75% by weight ofsaid mixture and the concentration of said acidic phosphorus portionbeing in a range from about 0.25 to about 2.4% by weight of saidmixture.

7. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p, p-dioctyldiphenyla-mine, theweight ratio of said N-ethylp'henothiaizne to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of butylacid phosphate, the concentration of said arylamine antioxidant portionbeing in a range from about 97.6 to about 99.75 by Weight of saidmixture and the concentration of said acidic phosphorus portion being ina range from about 0.25 to about 2.4% by weight of said mixture.

8. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p'dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of diphenylhydrogen phosphate, the concentration of said arylamine antioxidantportion being in a range from about 97.6 to about 99.75% by weight ofsaid mixture and the concentration of said acidic phosphorus portionbeing in a range from about 0.25 to about 2.4% by Weight of saidmixture.

9. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of methylacid phosphate, the concentration of said arylamine antioxidant portionbeing in a range from about 97.6 to about 99.75% by weight of saidmixture and the concentration of said acidic phosphorus portion being ina range from about 0.25 to about 2.4% by weight of said mixture.

10. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, theWeight ratio of said N- ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of 2,2-dimethyl-l ,3 -propanediol-cyclic-hydrogen-phosphite, the concentrationof said arylamine antioxidant portion being in a range from about 97.6to about 99.75% by weight of said mixture and the concentration of saidacidic phosphorus portion being in a range from about 0.25 to about 2.4%by weight of said mixture.

11. An antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,pdioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of diethylhydrogen phosphite, the concentration of said arylamine antioxidantportion being in a range from about 97.6 to about 99.75% by Weight ofsaid mixture and the concentration of said acidic phosphorus portionbeing in a range from about 0.25 to about 2.4% by weight of saidmixture.

12. An antioxidant composition comprising a mixture consistingasentially of (1) an arylamine antioxidant portion consistingessentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, theweight ratio of said N- ethylphenothiazine to saidp,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of bis-(2-ethylhexy1)hydrogen phosphite, the concentration of said arylamineantioxidant portion being in a range from about 97.6 to about 99.75% byweight of said mixture and the concentration of said acidic phosphorusportion being in a range from about 0.25 to about 2.4% by weight of saidmixture.

13. A11 antioxidant composition comprising a mixture consistingessentially of (1) an arylamine antioxidant portion consistingessentially of N-dodecylphenothiazine and p,p'-dioctyldiphenylamine, theweight ratio of said N-dodecylphenothiazine to saidp,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2,and (2) an acidic phosphorus portion consisting essentially of ethylacid phosphate, the concentration of said arylamine antioxidant portionbeing in a range from about 97.6 to about 99.75% by weight of saidmixture and the concentration of said acidic phosphorus portion being ina range from about 0.25 to about 2.4% by weight of said mixture.

14. A synthetic lubricant consisting essentially of (A) an organic esterbase stock and (B) at a concentration in a range from about 0.20 toabout 4.05% by weight of said organic ester base stock a mixtureconsisting essentially of (1) an arylamine antioxidant portionconsisting essentially of (a) N-alkylphenothiazine wherein the N- alkylgroup has 1-18 carbon atoms and (b) p,p-dialkyldiphenylamine wherein thep and p-alky1 groups each have 1-18 carbon atoms, the weight ratio ofthe N-alkylphenothiazine to the p,p'-dialkyldiphenylamine being in arange from about 1:3 to about 3:1, and (2) an acidic phosphorus portionconsisting essentially of ethyl acid phosphate, the concentration ofsaid arylamine antioxidant portion being in a range from about 95.3 toabout 99.95% by weight of said mixture and the concentration of saidacidic phosphorus portion being in a range from about 0.05 to about 4.7%by weight of said mixture.

15. A synthetic lubricant consisting essentially of (A) an organic esterbase stock and (B) at a concentration in a range from about 0.20 toabout 4.05% by weight of said organic ester base stock a mixtureconsisting essentially of (1) an arylamine antioxidant portionconsisting essentially of (a) N-alkylphenothiazine wherein the Nalkylgroup has 1-18 carbon atoms and (b) p,-p'- dialkyldiphenylamine whereinthe p and p-alkyl groups each have 118 carbon atoms, the weight ratio ofthe N-alkylphenothiazine to the p,p-dialkyldiphenylamine being in arange from about 2:3 'to about 3:2, and (2) an acidic phosphorus portionconsisting essentially of ethyl acid phosphate, the concentration ofsaid arylamine antioxidant portion being in a range from about 97.6 toabout 99.75% by weight of said mixture and the concentration of saidacidic phosphorus portion being in a range from about 0.25 to about 2.4%by weight of said mixture.

References Cited by the Examiner UNITED STATES PATENTS 2,743,234 4/1956Matuszak et al. 25246.7 2,930,758 3 1960 Tierney et al. 25246.73,038,858 6/1962 Verley 25247 3,038,859 6/1962 Eickemeyer et al. 25247FOREIGN PATENTS 847,399 9/ 1960 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

1. AN ANTIOXIDANT COMPOSITION COMPRISIN A MIXTURE CONSISTING ESSENTIALLYOF (1) AN ARYLAMINE ANTIOXIDANT PORTION CONSISTING ESSENTIALLY OF (A)N-ALKYLPHENOTHIAZINE WHEREIN THE N-ALKYL GROUP HAS 1-18 CARBON ATOMS AND(B) P,P''-DIALKYLDIPHENYLAMINE WHEREIN THE P AND P''-ALKYL GROUPS EACHHAVE 1-18 CARBON ATOMS, THE WEIGHT RATION OF THE (-ALKYL-PHENOTHIAZINETO THE P,P''-DIALKYLDIPHENYLAMINE BEING IN A RANGE FROM ABOUT 1:3 TOABOUT 3:1, AND (2) AN ACIDIC PHOSPHORUS PORTION CONSISITING ESSENTIALLYOF AT LEAST ONE ACIDIC PHOSPHORUS COMPOUND SELECTED FROM THE GROUPCONSISTING OF AN ALKYL ACID PHOSPHATE WHEREIN THE ALKYL GROUP CONTAINSFROM 1 TO 10 CARBON ATOMS, OPHOSPHORIC ACID, DIPHENYL HYDROGENPHOSPHATE, DIETHYL HYDROGEN PHOSPHITE, BIS(2-ETHYLTHEXYL)HYDROGENPHOSPHITE AND 2,2-DIMETHYL-1,3-PROPANEDIOL-CYCLIC-HYDROGENPHOSPHITE, THECONCENTRATION OF SAID ARYLAMINE ANTIOXIDANT PORTION BEING IN A RANGEFROM ABOUT 95.3 TO ABOUT 99.95% BY WEIGHT OF SAID MIXTURE AND THECONCENTRATION OF SAID ACIDIC PHOSPHORUS PORTION BEING IN A RANGE FROMABOUT 0.05 TO ABOUT 4.7% BY WEIGHT OF SAID MIXTURE.